The goal of this project is to determine the comparative structure of two carbohydrate binding lectins produced by invertebrate species and to identify sites responsible for their ligand binding activity. Initial and major emphasis will be given to primary structure determinations since knowledge of the amino acid sequence of these proteins will aid in the characterization of the ligand binding sites, will permit the discerment of possible homologous relationships both with other lectins of animal or plant origin, and with members of other protein families, and will provide a structural foundation for the possible use of these carbohydrate specific proteins as probes of normal and abnormal cell function. Because of their related specificity for sialic acid, two lectins have been selected for study in depth. Work on limulin from the horseshoe crab will be directed toward completion of its amino acid sequence, which is already well begun. A second sialic acid binding lectin from the lobster, Homarus americanus, will also be purified and sequenced for comparative purposes. Attention will also be given to the interaction of these two sialic acid binding lectins with the cell surface because of the previously established association of increased surface sialic acid with the tumor state in several systems. Because of their specificity, these lectins may ultimately be useful in monitoring significant cell surface changes associated with the neoplastic state. Attempts will also be made to conjugate another biologically active protein moiety (the complement binding CH2 domain of a human immunoglobulin molecule) to at least one of these lectins. Such a system could be a useful model for systems designed to target various biologically active entities using proteins of known ligand binding specificity.